Generally, polyester drawn yarns used as industrial yarns are produced by a spinning and drawing process in which a quenching delay region I is mounted.
As a concrete conventional technique, as shown in FIG. 1, there has been used a method that improves drawing property by suppressing the orientation property of undrawn yarns, in which a quenching delay region I having a vertical array of a hood heater 2 and an insulating board 3 is mounted between a spinneret 1 and a quenching chamber 4.
In the above-stated conventional technique, a melt polymer extruded from a spinneret 1 is sequentially passed through a high temperature hood heater 2 and an insulating board 3 for monomer absorption and then solidified in a quenching chamber 4 that is mostly an open type, thereby preparing an undrawn yarn.
Then, a spinning oil is fed to the undrawn yarn and drawn with high drawing rate, thereby preparing a drawn yarn.
However, such a conventional method was problematic in that, if a spinning speed increases, a degree of orientation of the undrawn yarn increases, a solidification point is lowered, quenching is carried out non-uniformly and thus the uniformity between undrawn filaments are degraded.
With this degradation of the uniformity between undrawn filaments, the drawing property in a drawing process becomes poor and results in the generation of noils to the drawn yarn and the degradation of quality.
Hence, in the conventional method, there is a limit to increase a spinning speed to more than a predetermined level, and accordingly there is also a limit to improve productivity.
On the other hand, in a polyester drawn yarn produced by the conventional method, a thermal relaxation stress change ratio and thermal relaxation stress area ratio on thermal relaxation and shrinkage stress curves are too large, thus the form of the polyester drawn yarn is easily changed by a heat and tension applied in an after-processing process.
In this way, in the event that the low-shrinkage polyester yarn has a reduced form stability against heat, there occurs a phenomenon that (hereinafter, referred to as a “wrinkle phenomenon”) a wrinkle is shown on a product in an after-treatment process for coating polyvinyl chloride (PVC) and this deteriorates the quality of the product.
It is an object of the present invention to provide a high strength low shrinkage polyester drawn yarn which is useful as industrial yarns such as seat belts, webbings, tarpaulins and so on because it shows superior form stability in an after-treatment process.
It is another object of the present invention to provide a process for producing a high strength low shrinkage polyester drawn yarn which can improve form stability against heat and tension, drawing properties and productivity by uniformly managing the solidification point of melt polymers even upon an increase of a spinning speed, uniformly managing a yarn tension during relaxing or making both solidification point and yarn tension during relaxing uniform.